MATRIX-ASSISTED-LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY AND ELECTRON-MICROSCOPY FOR THE CHARACTERIZATION OF THE VITELLINE COAT GLYCOPROTEINS OF THE POLARIZED EGG OF UNIO-ELONGATULUS/

The vitelline coat (VC) glycoproteins of the Unio elongatulus egg, pur ified as previously described (Focarelli and Rosati, 1993: Mol Reprod Dev 35:44-51) and indicated as gp220 and gp180 by virtue of their appa rent molecular weights in sodium dodecyl sulfate-polyacrylamide gel el ectrophoresis (SDS-PAGE), were analyzed by matrix-assisted laser desor ption/ionization mass spectrometry (MALDI MS). The analysis confirmed the purity of our preparations and the mass of gp180, but gave a mass of 273,000 for gp220. Intact VCs and purified VC components were then visualized in stereo images of platinum replicas produced by the quick -freeze, deep-etch, and rotary shadowing techniques: gp180 revealed a c-like shape and gp273 a rosette-like shape. The intact VCs were found to consist of two layers, the internal one clearly fibrous and the ex ternal one compact. Since purified preparations of gp180 spontaneously formed fibrils of similar width to those present in the inner VC laye r, this layer presumably consists mainly of this component. The preval ence of gp273 in the outer layer is also suggested and discussed. (C) 1997 Wiley-Liss, Inc.